This invention relates to an improved method for forming hollow articles from reheated injection molded thermoplastic preforms by injection molding said preforms using a selected mold distribution system.
It is known to thermoform molded, elongated, tubular thermoplastic preforms into hollow articles such as bottles and containers. One particularly desirable method for producing the preforms that are used is by injection molding since such method allows for the high production of parts having very uniform dimensions and weight distribution. A variety of mold distribution systems have been disclosed in the injection molding technology as disclosed for example in "Injection Molding Theory and Practice" by Irvin I. Rubin, 1972, chapter 2. One particularly attractive system involves the use of an insulated runner, however, the use of a cartridge heater or heated torpedo extending into the gate channel as commonly used in such a system, creates significant lean and distortion problems when reheating molded preforms. This lean causes thermoformed articles prepared from such preforms to have an undesirable variation in wall thickness and often the minimum acceptable limits will not be satisfied.